This invention relates to a method for separating trialuminum nickelide fibers from an aluminum matrix. More particularly, this invention concerns itself with the electrolytic production of trialuminum nickelide fibers from an aluminum/trialuminum nickelide two phase composite matrix.
Considerable interest has been developed in the utilization of aluminum nickel fibers. These fibers find application for use as catalysts, obfuscating agents, and as components for microelectronics. Their wide application results from the fact that inclusion of a controlled eutectic alloy of trialuminum nickelide within an aluminum body provides an effective means for giving high tensile strength enhancement to the aluminum body. The alloy is grown within the aluminum body as an aligned microstructure in the form of whiskers by a technique referred to as unidirectional solidification. In addition to providing improved tensile strength, the whiskers of trialuminum nickelide are useful, in and of themselves, in a variety of industrial and military microelectronic applications provided they can be removed undamaged from the aluminum matrix in which they are embedded.
A number of methods are utilized for producing trialuminum nickelide whiskers in aluminum matrix. One such method uses a unidirectional solidification technique. Another method involves the growth of aluminum nickel fiber bundles longitudinally in a rod shaped matrix. Still other methods are contemplated and a considerable research effort is being conducted in an attempt to develop even more efficient means of growing these useful fibers. However, a fundamental problem exists in the removal and separation of the fibers from the aluminum/trialuminum-nickelide two phase matrix within which they are grown. Therefore, a need exists for the development of an efficient and practical removal method in order to study the effectiveness of prior art growth procedures as well as those conceived in the future. Also, the usefulness of the individual fibers themselves for microelectronic applications is severely limited unless an efficient means can be developed for their removal from the aluminum matrix without encountering severe damage during the removal procedure.
In previous methods, aqueous electrolytes or acid etches were utilized for removing or dissolving the aluminum from the aluminum/aluminum-nickelide matrix. Unfortunately, these methods have always been accompanied by gas evolution resulting in "birdnesting" of the fiber bundles as they are exposed. Still another problem encountered in using aqueous acid etches was their low selectivity of attack. For example, the aluminum nickelide fibers were dissolved as well as the bulk aluminum. It became obvious, therefore, that an electrolyte that could sustain aluminum electrolysis without gas evolution while simultaneously committing selective attack on the bulk aluminum phase of the aluminum containing matrix would circumvent the problems encountered in using prior art methods of separation.
In attempting to overcome the problems encountered with prior art methods of separating aluminum from a two-phase matrix of aluminum and trialuminum nickelide filaments, a method was developed using an electrolytic procedure for etching away the trialuminum nickelide fibers previouly formed in the aluminum matrix. In the electrolytic etching procedure referred to, two molten salts containing aluminum chloride were utilized. This method proved quite successful; but, required an inert atmosphere and high temperature conditions as processing parameters. The high temperature conditions and inert atmospheric conditions required for use with this method posed serious processing problems and increased the overall cost of the unit operation.
With the present invention, however, it has been discovered that the problems encountered in prior art methods, as well as in prior art electrolytic procedures utilizing high temperture and inert atmospheric conditions could be overcome by a method which utilizes potassium hydroxide as the electrolyte. The method is carried out within a time period during which the aluminum nickelide fibers are not attacked by the potassium hydroxide. The process is inexpensive and is carried out under ambient conditions. It produces high quality fibers which cannot be duplicated by other methods.